The present invention relates to the field of separators and more specifically to means intended to separate droplets or particles of a gaseous stream, smaller than or of the order of one micrometer in size.
Many methods and devices have already been disclosed for this purpose.
U.S. Pat. No. 5,626,651 describes a process and a system of this type where the turbulent gas stream flows above a series of plates defining non-turbulent zones in which the particles are collected. More precisely, the plates are parallel to each other and vertical. A filtering means consisting of fibers can further be provided between said plates in order to improve filtering, notably of the finer particles.
International patent application WO-95/28,217 describes a device based on the is same principle, but in which the plates are provided with slots or replaced by grates. Carcasses made of wire mesh covering a fiber mat are furthermore used in this prior art.
Besides, patent application WO-97/00,102 relates to a separator placed at the exhaust of diesel engines, intended to collect the particles contained in the exhaust gases. A honeycomb structure pierced with channels perpendicular to the opening of the honeycomb cells is preferably provided. The porosity of such a structure is of the order of 70%. However, this device cannot be used for mists because the droplets captured in he cells cannot be drained off.
International patent application PCT/FR-97/00,164 relates to a separator for mists, having one or more vertical delivery channels laterally delimited by fibrous corrugated elements. An agglomerator is furthermore necessary upstream from the separator in order to have larger particles that can be separated in the separator. This is however relatively costly and implies considerable pressure drops.
However, these well-known means do not allow to efficiently collect and remove particles and/or droplets smaller than about one micrometer: in U.S. Pat. No. 5,626,651, the particles captured accumulate on the walls, then fall to the bottom of the device under the effect of gravity. Means intended to shake the walls are often necessary to cause the particles accumulated on the walls to fall. This device pose problems for separation of very fine particles smaller than one micrometer. In fact, in this case, the channel must be very small in height and therefore the plates very high so that the equipment is very bulky for a very small sectional area of flow. The same problem exists in the device according to document WO-95/28,217.
In patent application WO-97/00,102, the particles collected are oxidized.
The present invention proposes solving the problem of removal of particles and/or droplets smaller than or of the order of one micrometer in size in an original and unexpected way, as explained hereafter.
The present invention advantageously prevents any pressure drop due to clogging of zone of the device. The pressure drop remains constant throughout the life of the separator according to the invention.
The present invention allows to remove particles present for example in exhaust gases of vehicles equipped with diesel engines, in the dusts of more or less confined inner spaces, in fumes of all sorts such as metallurgical fumes, or acid fumes.
The global structure of the invention can be the structure described in patent application WO-97/00,102 or in French patent application EN.97/12,867 filed by the applicant. Other support materials can also be used as explained hereafter.
In relation to the devices listed above, the particle collection rate can be increased very significantly by means of the invention.
The object of the present invention is thus a mechanical separator intended to collect particles contained in gaseous effluents and smaller than or of the order of one micrometer in size, comprising at least one channel for turbulent flow of the effluents, preferably several parallel channels formed in a porous structure having particle collection surfaces, and whose points stick out irregularly.
The separator according to the invention further comprises a series of small elements made of ultrafine fibers, said elements being both permanently interlocked with each other and with the surface of said particle collecting surfaces, and whose points stick out irregularly.
More precisely, said fibers are of the order of one micrometer in diameter.
Furthermore, said fibers are less than about one millimeter in length.
According to the invention, said interlocked elements form a layer that is less than about one millimeter thick.
In accordance with an embodiment of the invention, the porous structure comprises a ceramic honeycomb.
According to another embodiment of the invention, the porous structure comprise a cross-linked polyurethane foam.
According to another embodiment of the invention, the porous structure comprises a ceramic cross-linked foam made from a group comprising alumina, cordierite, mullite, zirconia, sialon, silicon carbide.
More precisely, said ceramic cross-linked foam has a porosity ranging between 70% and 90%.
In particular, the length of the separator according to the invention ranges between about 10 cm and about 100 cm.
According to a particular embodiment of the invention, the separator comprises several parallel or substantially parallel channels.
The number of delivery channels is preferably proportional to the flow rate of the gaseous effluents.
The invention further relates to a process for manufacturing a separator as described above.
The process according to the invention comprises the following stages:
dipping a porous structure comprising delivery channels in a first solution,
taking said structure out of the first solution,
passing an air stream for about one hour through the channels of said structure,
dispersing small ultrafine fiber elements in the air stream
letting the small elements settle from the turbulent air onto the collecting surfaces, made adhesive, of the porous structure so that the points of the small elements stick out of the surface irregularly,
placing the separator in a drying oven for about one hour.
Furthermore, after the small fibrous elements have settled on the collecting surfaces, said channels are hollowed out on their initial inner section by cutting the small fibrous elements that stick out.
The first solution can consist of a mixture of Silane in a hydrocarbon solvent.
Without departing from the scope of the invention, said first solution can consist of a mixture of water, sodium silicate and ethylene glycol.